1. Field of the Invention
The present invention relates to a silver halide photographic emulsion which is spectrally sensitized with at least two sensitizing dyes having a super-sensitizing action. More particularly, the present invention relates to a silver halide photographic emulsion in which the spectral sensitivity of the silver halide in the green color wavelength region of the spectrum is increased.
2. Description of the Prior Art
It is well known to extend the photosensitive wavelength region of a silver halide photographic emulsion into a longer wavelength region by addition certain cyanine dyes thereto, i.e., spectral sensitization is used as one method of producig a photographic photosensitive material.
The spectral sensitivity is usually influenced by the chemical structure of the sensitizing dye and the properties of the emulsion such as the halogen composition, the crystal habit, the crystal system, the silver ion concentration, the hydrogen ion concentration and the like of the silver halide. Moreover, the spectral sensitivity is influenced by the sensitizer, the antifogging agent, the auxiliary coating agent, the precipitating agent, the color coupler, and the like which are generally present in the emulsion.
In general, a single sensitizing dye is used for sensitization of a given spectral wavelength region of a photosensitive material. Where such spectral-sensitizing dyes are used in admixture with each other, the spectral sensitivity produced is often lower than that produced by the sensitizing dyes individually. In some specific cases, however, the spectral sensitivity is superadditively increased by using a certain sensitizing dye in combination with at least one other sensitizing dye. This phenomenon is known as "supersensitization". A considerable selectivity is required in combining such sensitizing dyes and since the supesensitization is markedly influenced by a slight difference in the chemical structures of the sensitizig dyes used, it is difficult to predict a combination of sensitizing dyes exhibiting supersensitization only from the chemical structures of the sensitizing dyes.
The sensitivity produced by a certain dye is usually influenced by the type of the emulsion to which the dye is added, and particularly, the halogen composition, the crystal habit, the crystal system, and the like of the silver halide.
Moreover, the sensitivity of a given emulsion can be changed by changing the state of the emulsion. For instance, the sensitivity can be increased by increasing the silver ion concentration, or decreasing the hydrogen ion concentration, or effecting these changes simultaneously. Thus, the sensitivity can be increased by immersing a film with a spectral-sensitized emulsion coated thereon in water or an aqueous ammonium solution. The above described methods wherein the sensitivity of a sensitized emulsion is changed by increasing the silver ion concentration, or decreasing the hydrogen ion concentration, or effecting these changes simultaneously, are generally called hypersensitization. A hypersensitized emulsion generally has a short storage life.
The requirements for the sensitizing dye used in applying the supersensitization to the silver halide photographic emulsion are: the sensitizing dye does not adversely interact with photograhic additives other than the sensitizing dye, and the sensitizing dye possesses stable photographic characteristics during the storage of the photosensitive material.
Another requirement for the sensitizing dye is that no residual coloring due to the sensitizing dye remains in the photosensitive material after processing. It is particularly required that the sensitizing dye leaves no residual coloring on processing in a short time, generally several seconds to several ten seconds, such as in rapid processing.
At the present time, for spectral sensitization in the green color wavelength region, oxacarbocyanine based dyes, imidacarbocyanine based dyes, 2,2'-thiacyanine(pseudo) based dyes, and dimethinemerocyanine based dyes are used, alone or in admixture with each other. The silver halide emulsion spectral-sensitized with these sensitizing dyes is applicable to a green photosensitive layer for color photography, a lith type orthochromatic photosensitive material for plate making, an indirect X-ray photographic material wherein an X-ray image is projected on a fluorescent plate and photographed, and a photosensitive material for use in a cathode ray tube display system.
In the green sensitive layer, it is preferred that the longer wavelength part overlap the shorter wavelength part of the red sensitive layer less because less overlap reduces color mixing.
In the litho type film and the indirect X-ray film, it is desired that the processing including the development and fixing be carried out in a well-lighted room. These photosensitive members are processed under a safe light as passed through a No. 6 or No. 7 Safe Light Filter produced by Fuji Photo Film Co., Ltd., or under a similar safe light. To increase the safe light stability, it is advantageous that the longer wavelength part of the spectral sensitivity be shifted to as short a wavelength side as is possible.
Thus, spectral sensitization in which the photosensitive longer wavelength part is present at a relatively shorter wavelength and which can provide high green sensitivity, has been desired.